1. Field of the Invention
The present invention relates to a fixing device to be used in an electrophotographic image forming apparatus such as a copying machine or a printer.
2. Description of the Related Art
In some cases, a film heating type fixing device, which is advantageous from the viewpoint of quick start or energy saving, is used as a fixing device for an image forming apparatus such as a copying machine or a printer.
The above-mentioned fixing device includes a heat resistant film (hereinafter simply referred to as a film), a heater, and a pressure member forming a nip portion together with the heater via the film. It is common practice to heat a recording material bearing an unfixed toner image at the nip portion while conveying the recording material, thereby fixing the toner image to the recording material.
In this film heating system, there can occur, due to variation in positional accuracy of the film and the pressure member, a phenomenon (hereinafter referred to as a film deviation) in which the film is allowed to deviate in a direction (film generatrix direction) orthogonal to the recording material conveyance direction. As a countermeasure for this film deviation, there is adopted a method in which an edge portion of the film is regulated by a regulating member.
However, when the edge portion of the film is regulated by the regulating member, there may be generated bend, wrinkle, and fissure (hereinafter referred to as a film edge portion damage) due to the film deviation force.
In view of this, Japanese Patent Application Laid-Open No. 5-208750 discusses a fixing device employing a regulating member having a regulating surface such that a distance from an imaginary plane perpendicular to the longitudinal direction of the film is decreased immediately after the nip portion toward the downstream side in the film moving direction, and a regulating surface continuous with the above-mentioned regulating surface and perpendicular to the longitudinal direction of the film. Due to the above regulating member, the film edge portion gradually receives a reaction force of the film deviation force from the regulating surface, thereby suppressing a film edge portion damage.
However, the above-described construction has often proven insufficient in suppressing the film edge portion damage generated by a deviation force applied to the film when a user pulls the recording material out of the nip portion.
This is because the strength of the film deviation force in coping with a jam depends on the force with which the user pulls the recording material out of the nip portion and the angle at which the recording material is pulled out, and, in some cases, there can be generated a deviation force larger than that at the time of fixing.